28 MEMOIRS OF THE QUEENSLAND MUSEUM. 



type, as illustrated by Atlantochelys mortonii, Agassiz, although the absence 

 of the radial process prohibits adequate comparison. Wieland also notes 

 resemblance between Atlantochelys and Desmatochelys lowii, Williston. 8 



Radius and Vina. — About 12 centimetres of the proximal ends only are 

 preserved, and the ectal surfaces of these are incomplete. The proportions of 

 these bones are considerably in excess of the relations borne to C. mydas by the 

 other fragments ; from this one may infer very powerful fore-limbs and nippers. 

 The robustness of the front nippers in Toxochelys and Archelon has been 

 demonstrated by Wieland, 9 who, after comparing the Cretaceous remains with 

 those of present-day carnivorous and algaphagous turtles, says: " There is in 

 the comparison just made the very strongest suggestion that Protostega, more 

 distinctly than any marine turtle thus far known, hunted prey, which swam 

 actively, and, bearing in mind other features, was perhaps even powerful. ' ' 



When compared with corresponding portions of a large skeleton of Chelone 

 mydas, representing an individual about 5 feet 9 inches, our fossil bones, except 

 where noted, are a little more than twice the size. Following out these pro- 

 portions, a turtle nearly 12 feet in length is suggested. Some specimens of the 

 genus Archelon, described by Wieland, were about 13 feet in length. 



Plastral Plate (PI. XII and XIII). — The evolution of the dermal armours 

 of Chelonians is one of the most perplexing yet fascinating problems to be 

 elucidated by palaeontologists, and the researches of such writers as Wieland 

 and Hay in America are here of great value. The plastral plate is therefore the 

 most interesting bone in the collection, and it is a matter for deep regret that the 

 portion preserved is so incomplete. Of this fragment the greatest length is 51 

 centimetres and the greatest breadth 22 centimetres. The thickness is exceedingly 

 variable, the maximum — 33 millimetres — being in the centre on the left of the 

 longer axis. From below this and to the right the plate shelves away and 

 terminates in dactyloid processes. The broken ends of two dactyloid processes 

 are exposed on the lower side of the plate to the right. (See PI. XII.) It has 

 been possible only partially to remove the matrix at this part, but the course of the 

 processes is now apparent. The lowest digit is broken across 60 mm. from its 

 base, but the upper, running apparently parallel to it at a distance of but 10 mm., 

 extends for 130 mm. to its exposed fracture. During fossilisation this digit has 

 evidently been broken, and the distal portion is partly superimposed not far 

 from the base. The course of these processes is almost parallel to the long axis 

 of the plate. On the ental side immediately above these broken digits is a furrow 

 almost deep enough to appear through the plate, and this points to another 

 dactyloid process more robust than the ones seen in situ. Within the margin of 

 the anterior edge of the plate on the right are two other furrows, marking the 

 bases of still stronger dactyloid processes, and the adjoining anterior border is 

 chamfered away to a thin edge. (PI. XIII.) 



8 Williston, Univ. Kansas Geol. Sur., vol. iv., Pal., 1898. 



Wieland, Mem. Carnegie Museum, vol. ii., No. 7, 1906, p. 289. 



